1. Field of the Invention
The present invention relates to the art of compressing a refrigerant gas in an electric motor driven compressor. More particularly, the present invention relates both to providing refrigerant gas at a pressure intermediate the compressor suction and discharge pressures to the working chamber of a compressor in a refrigeration system while simultaneously cooling the compressor drive motor all in a single housing. With even more particularity, the present invention relates to cooling the drive motor of a screw compressor in a refrigeration system with liquid refrigerant, while simultaneously directing refrigerant which has flashed into gas within the drive motor housing, together with gas generated by drive motor cooling, into the compression chamber of the compressor assembly within the system.
2. Description of Prior Art
The substantial advantages relating to increasing the efficiency and capacity of a refrigeration system by economizer coupling are well documented. Refrigeration systems in which screw compressors are employed are particularly amenable to economizer coupling by virtue of the geometry of the rotors and compression chamber found therein. Two complementary rotors are located in the compression or working chamber of a screw compressor. The motor which drives the rotors is normally located in a second housing attached to but sealed from the housing which defines the compression chamber. Refrigerant gas is received at low pressure and enters the suction port of a screw compressor where it is enveloped in a pocket formed between the compressor rotors. The volume of this pocket decreases and the pressure therein rises as the rotors rotate and mesh. The pocket is circumferentially displaced and eventually opens to the discharge port at the high pressure end of the compressor.
When an economizer vessel is employed and disposed in a refrigeration circuit, refrigerant gas generated within the economizer vessel is delivered to the working chamber of the compressor at a location where the pressure within the working chamber is intermediate the suction and discharge pressure of the compressor. The delivery of such gas, called economizer coupling, is advantageous in that the refrigeration capacity of the system is increased to an extent which more than offsets the increased power consumption needed to compress the additional amount of gas delivered to the compression chamber. The use of refrigerant gas produced in an economizer vessel disposed in a refrigeration system to cool the motor of the refrigerant compressor therein is known. U.S. Pat. No. 3,913,346 to Moody, Jr. et al discloses the use of refrigerant to cool the drive motor of a screw compressor and recites a concise litany of pertinent previously patented compressor motor cooling schemes. In the Moody, Jr. et al patent a portion of the liquid refrigerant produced in a condenser and flash gas produced in an economizer vessel are separately directed into a compressor motor housing. Liquid refrigerant delivered from the compressor drive motor housing is fed into the compression chamber to cool the compressor rotors. Vanes attached to the motor rotor splash liquid refrigerant, which is accumulated in the lower portion of the motor housing, over the motor stator to accomplish motor cooling. In U.S. Pat. No. 2,921,446 flash gas is directed from an economizer vessel into the sealed motor housing of a centrifugal refrigerant compressor. After passing through the compressor motor and motor housing the refrigerant gas, which has expanded in the course of motor cooling, is directed into the working chamber of the compressor. U.S. Pat. No. 3,388,559 discloses an installation in which a portion of the refrigerant exiting the condenser in a refrigeration circuit is metered into the housing of a compressor motor by an expansion valve dedicated to the motor cooling task. The refrigerant expands in the motor housing while cooling the compressor motor and is thereafter returned to the suction gas line in the refrigeration circuit. Likewise, U.S. Pat. No. 3,945,219 describes an installation in which a portion of the refrigerant exiting the condenser of a refrigeration circuit is metered into the compressor drive motor housing by a throttling device dedicated to the accomplishment of compressor motor cooling. The refrigerant metered into the compressor motor housing expands as it cools the compressor motor, mixes with compressor motor lubricant and together with the lubricant is directed into the working chamber of the screw compressor driven by the motor.
As is suggested by the wealth and diversity of compressor motor cooling schemes found in the prior art, a continuing need exists both for continued improvements in the implementation of economizer coupling and for a more economical and efficient method and apparatus by which the cooling of the motor driving a refrigeration compressor is accomplished.